1. Field of the Invention
The present invention relates to an image signal recording and reproducing apparatus which compresses an image signal for color display and records the compressed image signal in magnetic recording media. The present invention further relates to an image signal recording and reproducing apparatus which can easily record an image signal for color display.
2. Description of the Related Art
In an imaging device, such as a TV camera using a CCD image sensor, horizontal and vertical scanning timings are determined based on various synchronizing signals according to a predetermined television format. As a result of scanning an object at determined timings, image information for one image picture, or one scene, is gathered, and transformed in order to be conveyed by successive image signals arranged in a predetermined order.
FIG. 19 is a block diagram representing a basic structure of an imaging device using a CCD image sensor; FIG. 20 is a diagram indicating operation timings of the device of FIG. 19.
A CCD image sensor 1 of a frame transferring type comprises an imaging device 1i, a storage 1s, a horizontal slider 1h, and an output section 1d. An imaging device 1i consists of a plurality of CCD shift registers which are arranged parallel to each other and successive in the vertical direction. Each bit of the respective shift registers constitutes a light receiving pixel element for storing information charges generated while taking images.
Storage 1s, comprising a plurality of CCD shift registers having as many bits as those of the sensor 1, is continuous with the shift registers of the imaging device 1i. Each bit of the respective shift registers temporarily stores the image charges supplied from each light receiving pixel element of the imaging device 1i.
The horizontal slider 1h, comprising a single CCD shift register each bit of which is coupled to an output of each shift register of the storage 1s, sequentially shifts the information charges supplied for every horizontal line from the storage 1s, toward the output section 1d.
The output section 1d is located on the output side of the horizontal slider 1h, and has a capacity for receiving information charges slid toward the output section 1d. The section 1d generates a voltage whose value varies depending on the amount of supplied information charges. The variation serves as an image signal 10.
A driver circuit 2 comprises a frame clock generator 2f, a vertical clock generator 2v, a horizontal clock generator 2h, and a reset clock generator 2r. The frame clock generator 2f generates a frame clock .phi.f in response to a frame shift timing signal FT, and supplies the clock .phi.f to the imaging device 1i so that information charges stored in the respective light receiving pixel element of the imaging device 1i are transferred to the storage 1s at high speed each vertical scanning period.
The vertical clock generator 2c generates a vertical clock .phi.v in response to a vertical synchronizing signal VT and a horizontal synchronizing signal HT, and supplies the signal .phi.v to the storage ls so that the storage 1s tentatively stores the image charges supplied from the imaging device 1i, and forwards the charges further to the horizontal slider 1h for every horizontal scanning line in every horizontal scanning period.
The horizontal clock generator 2h generates a horizontal transfer clock .phi.h in response to a horizontal synchronizing signal HT, and supplies the signal .phi.h to the horizontal slider 1h so that the slider 1h sequentially slides the information charges supplied from the storage 1s for every horizontal line toward the output section 1d.
A reset clock generator 2r generates a reset clock .phi.r, and supplies the clock .phi.r to the output section 1d so that the information charges slid by the horizontal slider 1h toward the output section 1d for every pixel, are stored in the output section 1d and then outputted in synchronism with the operation of the horizontal clock generator 2h.
A timing control circuit 3, which operates based on a reference clock having a constant cycle, generates a vertical synchronizing signal VT and a horizontal synchronizing signal HT for determining the timings at which the image sensor 1 executes vertical and horizontal scanning, and supplies the signals to the driver 2. The circuit 3 also generates a frame shift timing signal FT having the same cycle as that of a vertical synchronizing signal VT, and supplies the signal FT to the driver circuit 2. The timing control circuit 3 is responsible for a shutter control so as to keep the image sensor 1 in the optimum exposure state. Specifically, the circuit 3 instructs the imaging device 1i to output, during a vertical scanning operation, information charges stored therein, according to the amount of information charges caused and stored thus far in the imaging device 1i. That is, when the circuit 3 sets a faster shutter operation timing for outputting information charges from the imaging device 1i, information charges stay in the imaging device 1r in a longer period of time. On the other hand, when the circuit 3 sets a slower shutter timing, information charges stay in the imaging device 1r in a shorter period of time before an image taking operation is conducted with respect to the next picture frame before long. Note that a shutter operation is executed according to a driver clock supplied to the image sensor 1 by the driver circuit 2 to the image sensor 1.
An image signal I0 obtained through the above processes is supplied to a conventional television monitor or a recording device to be used for repeatedly displaying object images in the unit of an image picture at a frame rate determined corresponding to a vertical synchronizing signal VT.
It has also been attempted to input an image signal obtained by an imaging device into a personal computer or the like, as digital imaging device, to be used for displaying an image on the monitor screen thereof. An image obtained by an imaging device is seldom displayed on a full screen. Rather, it is generally compressed to be display a small image on the screen. As an image format adaptable to such a displaying manner, Common Intermediate Format (CIF) (352.times.240 pixels) and Quarter CIF (QCIF) standards (176.times.120 pixels) are available. CIF defines a size about a quarter of that of the Video Graphic Array (VGA) standard (640.times.480 pixels), which is one of the major personal computer monitor standards; QCIF define a size about a quarter that of the CIF standards. These standards are becoming widely accepted.
In an imaging device employing CIF or QCIF, the number of pixels according to the respective standards are installed into the image sensor. With these devices, the cost of an imaging unit is smaller than for conventional imaging devices adopted to general television formats, such as NTSC or PAL.
However, a recording format dedicated to imaging devices, such as the VHS format available for NTSC, has yet to be proposed for CIF or QCIF. Therefore, it has long been desired to determine a format in which image signals are recorded so as to be adopted to the above devices.
Conventionally, a digitally converted image signal is inputted into a computer device in a predetermined format, and stored in a recording means incorporated into or connected to the computer device. However, the imaging device must remain continuously connected to the computer in this method in order to introduce an image signal from the device to a computer. This is quite inconvenient.